Messing around with the fan speed to make it quieter is only going to make the card run at hotter temperatures, and with Turbo Boost 2.0, decrease its performance.
I think you are probably overestimating how quiet a video card should be. They can be heard and sometimes they can get sort of loud under normal circumstances. You may also be in a room with a warmer summer temperature, which is going to cause the fans to run faster and louder. The best thing to do is to make sure that your case is cleaned out and free of dust. Then consider upgrading your case fans or adding another to help cool the card.
Of course, I'm just assuming you don't have a defective fan on your card. If you could tell us how fast your fans are running when gaming, that would help. You can use Afterburner or PrecisionX to tell Fan % and RPMs.